As with some of the ideas on this site, I thought of this one after watching a show about how to stop asteroids from colliding with earth.

It sounds like billions of dollars, if not trillions are needed to fund a system that tries to scan for possible earth-bound asteroids, and secondly for a system
to knock them off a collision course. Perhaps governments all over the planet should excise a very small tax to help fund what could benefit all of human kind (and plant/animal kind minus the cockroach).

WEll, if we find one coming towards us, then at least all the raw material is heading in the right direction. That'll make it cheaper to mine. So it's not so much a tax, more like owning shares: we look for the thing, then when we find it we launch lots of little robot wizards (all based on the microsoft paperclip, because of its amazing flexibility and versatile nature, and because the sooner we get it off the planet the better), which dig like mad, refine the asteroid as best they can, then tweak its trajectory so it heads into a stable orbit! Hey presto, all the iron and rare metals you could ever want. If this all sounds expensive, then remember - it's not being funded out of your tax money - you own shares! And if it works you'll all be rich.

There already is a publicly-funded program to track asteroids. As to the second part, the system to knock them out, if people built an asteroid-smasher on the off-chance, they'd soon get bored with having it and not using it, and find alternative uses for it, like smashing up the moon or destroying Belgium.